1. Field of the Invention
The present invention relates to a polysilane composition useful as a material for forming core and cladding layers of a polymer optical waveguide, an optical waveguide fabricated using the polysilane composition and a method for fabrication of the optical waveguide.
2. Description of the Related Art
Polymer waveguides can be supplied in larger sectional areas and fabricated by simple techniques and at low costs. Because of such advantages, their practical application has been expected. Polymer waveguides are typically built by providing cladding layers in a manner to surround a core layer. In general, the core layer is laterally surrounded by a lateral cladding layer and flanked on its vertical sides by an upper cladding layer and a lower cladding layer. For example, a polymer optical waveguide is proposed which uses a polysilane compound for such core and lateral cladding layers (Japanese Patent Laying-Open No. 2002-311263).
Conventionally, the use of a single-mode optical fiber has been a mainstream of an optical communication system. This has led to extensive research and development of single-mode optical waveguides. A single-mode optical waveguide provides easy control of guided light, is advantageous in miniaturizing a device and is suited for high-speed operation.
However, the recent rapid rise of multi-media demands high-speed transfer of optical signals to offices and houses. Under such circumstances, a multi-mode optical waveguide is gaining an increasing attention as an inexpensive optical part.
Because core and lateral cladding layers in multi-mode optical waveguides generally have large thickness dimensions, the use of conventional polymer materials for those layers results in the failure to achieve uniform photobleaching in the formation of the lateral cladding layer, which has been a problem.
In order to solve the above-described problem, Japanese Patent Laying-Open No. 2004-333883 proposes the use of a polysilane composition containing a polysilane compound, a silicone compound and an organic peroxide in the formation of core and lateral cladding layers. The use of such a polysilane composition enables short-time and uniform photobleaching of the lateral cladding layer even if having a thickness of 20 μm.
However, the use of this polysilane composition results in problematic failure to simultaneously achieve optimization of a core shape and minimization of a propagation loss and a coupling loss. That is, a higher proportion of the polysilane compound improves a core shape but increases the propagation loss and coupling loss. On the other hand, a lower proportion of the silicone compound or a lower prebaking temperature, in the attempt to reduce those losses, softens a film. Then, a core goes out of shape to result in the problematic failure to obtain a satisfactory core shape.